explain whats the difference between modernism and postmodern in theatre?

Answer 1

Modernism tends to be a commentary on society or something in it, or a rebellion against something in it, it's a reaction, an effort to address social problems, or break down barriers of thought.
PostModernism breaks away from that artistic/social commentary, it rejects modernism.
Hope that helps.

Answer 2

do websearches of your terms.